Dialkylzinc composition having improved thermal stability

ABSTRACT

Anthracene compounds are added to dialkylzinc compositions to improve the thermal stability of the compositions.

BACKGROUND OF THE INVENTION

The present invention relates to dialkylzinc compositions havingimproved thermal stability. More particularly, the present inventionrelates to compositions comprising a dialkylzinc compound in admixturewith a stabilizer which reduces the thermal decomposition rate of thedialkylzinc compound.

Dialkylzinc compounds, particularly diethylzinc, are known to be usefulas polymerization catalysts in Ziegler-Natta type systems, as chemicalintermediates as well as alkylating agents. In addition, diethylzinc hasbeen found useful as a preservative for paper, which can be applied toexisting books and the like to extend their useful life, as is reportedin the October 1979 issue of "Chemical and Engineering News".

Unfortunately, however, the dialkylzinc compounds in addition to beingpyrophoric and highly reactive with water, are thermally unstable andcan decompose rapidly at elevated temperatures. The decomposition isexothermic, and could therefore become a "runaway reaction" unlessspecial precautions are taken to prevent it. Thus, for example, aquantity of this material in storage could slowly increase intemperature, due to slow decomposition, until a point was reached wherethe decomposition rate increased to a level which could present ahazard.

It has been reported, for example, that the half-life of diethylzinc is10 days at 120° C., about 1 day at 150° C. and only a few minutes at200° C.

The thermal instability of these compounds has been a significantdeterrent to their use because measures required to prevent thepossibility of a runaway reaction sometimes outweigh the benefits to beachieved.

If, however, the dialkylzinc compounds could be stabilized againstthermal decomposition so that their decomposition rates were moremanageable, the use of these compounds would be far more attractive.

A need therefore exists for a method by which the thermal decompositionrates of dialkylzinc compounds can be reduced.

It has now been found that the addition of anthracene compounds todialkylzinc compounds substantially reduce their rates of thermaldecomposition.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a process forimproving the thermal stability of a dialkylzinc compound represented bythe formula

    R--Zn--R

wherein R represents an alkyl radical having from 1 to about 8 carbonatoms which comprises adding to the dialkylzinc compound an anthracenecompound represented by the formula ##STR1## wherein each R¹independently represents an alkyl radical, an olefin radical conjugatedwith the aromatic moiety, an aryl radical or a substituted aryl radical,each having from 1 to about 12 carbon atoms, or hydrogen; in an amountsufficient to reduce the thermal decomposition rate of the dialkylzinccompound.

In accordance with another aspect of the present invention there isprovided a dialkylzinc composition having improved stability againstthermal decomposition comprising a dialkylzinc compound represented bythe formula

    R--Zn--R

wherein R represents an alkyl radical having from 1 to about 8 carbonatoms, in admixture with an anthracene compound represented by theformula ##STR2## wherein each R¹ independently represents an alkylradical, an olefin radical conjugated with the aromatic moiety, an arylradical or a substituted aryl radical, each having from 1 to about 12carbon atoms, or hydrogen; said anthracene compound being present in anamount sufficient to reduce the thermal decomposition rate of saiddialkylzinc compound.

DETAILED DESCRIPTION OF THE INVENTION

More in detail the dialkylzinc compounds which are stabilized inaccordance with the present invention are represented by the formula

    R--Zn--R

wherein R represents an alkyl radical having from 1 to about 8 carbonatoms. These compounds include, but are not limited to dimethylzinc,diethylzinc, dibutylzinc, diisopropylzinc, and diisobutylzinc; althoughdiethylzinc is preferred.

The anthracene compounds which are used are represented by the formula##STR3## wherein each R¹ independently represents an alkyl radical, anolefin radical conjugated with the aromatic moiety, an aryl radical or asubstituted aryl radical, each having from 1 to about 12 carbon atoms,or hydrogen. A particularly preferred anthracene compound is anthracene.

The anthracene stabilizer can be added to the dialkylzinc by anyconventional method, although the special handling requirements for thepyrophoric dialkylzinc compounds should be observed.

The amount of anthracene compound which is added is an amount which issufficient to achieve the desired degree of stabilization. When, forexample, the dialkylzinc compound being stabilized is diethylzinc, andthe anthracene compound being used is anthracene, effective amounts ofanthracene range from about 3% to about 5% by weight of diethylzinc.

The dialkylzinc compounds are shipped and used in industrial processeseither neat, or diluted with hydrocarbon solvents. Hydrocarbon solutionsof dialkylzinc compounds, particularly diethylzinc, typically range inconcentrations from 5% up to 50% by weight. Solvents employed include,but are not limited to pentane, hexane, heptane, toluene and xylene.These solvents are, of course, dried before using because dialkylzinccompounds react with water.

The present invention may be practiced with either the neat dialkylzinccompound, or with the diluted forms.

In order that the present invention be more fully understood, thefollowing Examples are given by way of illustration. No specific detailsor enumerations contained therein should be construed as limitationsexcept insofar as they appear in the appended claims. All parts andpercentages are by weight unless otherwise specifically designated.

EXAMPLE 1

A computer-controlled adiabatic calorimeter was used to determine thetime required for the decomposition of diethylzinc to become a runawayreaction at various temperatures under adiabatic conditions. The resultsare shown in Table I below.

                  TABLE I                                                         ______________________________________                                        TIME TO A RUNAWAY REACTION FOR THE                                            ADIABATIC DECOMPOSITION OF DIETHYLZINC                                        Temperature  Time to a Runaway                                                °C.   Reaction                                                         ______________________________________                                         80          124.3         days                                                90          33.6          days                                               100          9.8           days                                               110          3             days                                               120          23.5          hours                                              130          7.5           hours                                              140          2.5           hours                                              ______________________________________                                    

This demonstrates the thermal instability of diethylzinc.

EXAMPLE 2

Samples of diethylzinc were placed in a 300 ml. glass lined autoclaveequipped with an internal thermocouple and pressure transducer. Theautoclave was then equilibrated to room temperature, after which it washeated to increase the temperature of the contents at the rate of about5° per minute. The temperature and pressure inside the autoclave werecontinuously measured. The results of this test are summarized in TableII below.

                                      TABLE II                                    __________________________________________________________________________    SUMMARY OF DIETHYLZINC CONFINEMENT TESTS                                      Wt. of Exotherm*           Maximum Rate of                                                                         Moles of Gas                                                                           Maximum Rate                    Diethylzinc                                                                          Initiation                                                                          Maximum                                                                             Max. Pressure                                                                         Pressure Rise                                                                           Generated per                                                                          of Gas Generated                loaded (gms)                                                                         Temp. °C.                                                                    Temp. °C.                                                                    PSIG                                                                              ATM psi/sec                                                                           ATM/sec                                                                             Mole of DEZ (1)                                                                        moles/sec/mole                  __________________________________________________________________________    15     248   285    680                                                                               47  270                                                                              18    2.4      1.01                            60     207   423   2750                                                                              188 1435                                                                              98    1.7      1.02                            __________________________________________________________________________     *In one previous run, the start of rapid pressure rise occurred at            120° C.                                                                (1) DEZ: Diethylzinc                                                     

This Example shows that the thermal decomposition of diethylzinc inconfinement can result in substantial pressure generation. It also showsthat the rate of pressure rise is dependent on sample size, but that themoles of gas generated per second for each mole of diethylzinc isindependent of sample size and is on the order of 1.01 molesgas/second/mole of diethylzinc.

EXAMPLE 3

Using the same equipment and procedure as in Example 2, samples ofdiethylzinc were tested both with and without the additives listed inTable III. The results of these tests are shown in Table III.

                                      TABLE III                                   __________________________________________________________________________    SUMMARY OF DIETHYLZINC CONFINEMENT TESTS                                      Wt. of              Exotherm                    Moles of                                                                             Max. Rate of           Diethylzinc         Initi-                                                                              Max.                                                                              Max.    Maximum Rate of                                                                         generated                                                                            Gas Generation         loaded   Addi-      ation Temp.                                                                             Pressure                                                                              Pressure Rise                                                                           mole of                                                                              Moles/sec/mole         Run                                                                              gms   tive       Temp. °C.                                                                    °C.                                                                        PSIG                                                                              ATM psi/sec                                                                           ATM/sec                                                                             Diethylzinc                                                                          of                     __________________________________________________________________________                                                           Diethylzinc            1  15        none   248   285 680 47  270 18    2.4    1.01                   2  60        none   207   423 2750                                                                              188 1435                                                                              98    1.7    1.02                   3  60    5%  Acenaphthy-                                                                          200   413 940 65  42  3     0.58   3.1 ×                                                                   10.sup.-2                           lene                                                             4  68    ˜5%                                                                         Acena- 208   499 1710                                                                              117 293 20    0.83    0.176                              phthene                                                          5  60    ˜1%                                                                         Anthra-                                                                              193   405 >5000                                                                             341 1995                                                                              136   >3.2   1.42                                cene                                                             6  23    ˜3%                                                                         Anthra-                                                                              ˜210                                                                          419 490 34  ˜5                                                                          0.3   0.9    1.1 ×                                                                   10.sup.-2                           cene                                                             7  32    ˜5%                                                                         Anthra-                                                                              195   404 480 34  4.3 0.3   0.6    6.5 ×                                                                   10.sup.-3                           cene                                                             8  60    ˜5%                                                                         Anthra-                                                                              210   383 850 59  16  1.0   0.55   1.2 ×                                                                   10.sup.-2                           cene                                                             __________________________________________________________________________

This Example demonstrates that the addition of from about 3% to about 5%anthracene to the diethylzinc reduces the gas generation rate by afactor of about 100 to 150.

It will thus been seen that the process and composition set forth havedesirable advantages over the prior art. Since certain changes may bemade in the process and composition without departing from the scope ofthe invention, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

What is claimed:
 1. A dialkylzinc composition having improved stabilityagainst thermal decomposition comprising a dialkylzinc compoundrepresented by the formula

    R--Zn--R

wherein R represents an alkyl radical having from 1 to about 8 carbonatoms, in admixture with an anthracene compound represented by theformula ##STR4## wherein each R¹ independently represents an alkylradical, an olefin radical conjugated with the aromatic moiety, an arylradical or a substituted aryl radical, each having from 1 to about 12carbon atoms, or hydrogen; said anthracene compound being present in anamount sufficient to reduce the thermal decomposition rate of saiddialkylzinc compound.
 2. The dialkylzinc composition of claim 1 whereinR represents an ethyl radical and said dialkylzinc compound isdiethylzinc.
 3. The dialkylzinc composition of claim 2 wherein saidanthracene compound is anthracene.
 4. The dialkylzinc composition ofclaim 3 wherein said anthracene is present in an amount ranging fromabout 3% to about 5% based on the weight of dialkylzinc compoundpresent.
 5. A process for improving the thermal stability of adialkylzinc compound represented by the formula

    R--Zn--R

wherein R represents an alkyl radical having from 1 to about 8 carbonatoms which comprises adding to said diethylzinc compound an anthracenecompound represented by the formula ##STR5## wherein each R¹independently represents an alkyl radical, an olefin radical conjugatedwith the aromatic moiety, an aryl radical or a substituted aryl radical,each having from 1 to about 12 carbon atoms, or hydrogen; in an amountsufficient to reduce the thermal decomposition rate of said dialkylzinccompound.
 6. The process of claim 5 wherein R represents an ethylradical and said dialkylzinc compound is diethylzinc.
 7. The process ofclaim 6 wherein said anthracene compound is anthracene.
 8. The processof claim 7 wherein said anthracene is present in an amount ranging fromabout 3% to about 5% based on the weight of dialkylzinc present.